So far the broken servo arm count is 2!
The holes in the servo arms for the HXT900s are smaller than for the HD1900s. Tried using a screwdriver to widen the holes and start the screw...didn't work well; tried a screw with larger threads for more bite...cracked the arm; tried widening the hole with a hobby knife...success!, one ball in...then I cracked another arm...
I am going to get a very small drill bit and make the holes larger. Tried using the arms from the HD1900 servos but they won't fit the HXTs.
Have I properly expressed my dislike for servos yet? These things have delayed my build at least a week!